There is a conventionally known rotor of this type including permanent magnets bonded to a rotor body made of a steel using a synthetic resin adhesive (see Japanese Patent Application Laid-open No.4-101640).
The reason why the synthetic resin adhesive is used as described above is that a permanent magnet, particularly a permanent magnet including a rare earth element or elements is very brittle, resulting in a poor mechanical workability and has a nature that if when is exposed to a high temperature, its metallographic structure is changed and as a result, the magnetic characteristic is influenced. For this reason, in mounting the permanent magnets to the steel rotor body, a mounting means such as a dovetail-fit structure, screwing, welding and the like cannot be employed.
However, the bonding using the synthetic resin is accompanied by a problem that the temperature of the rotor rises with operation of the rotating machine, and if the temperature of the rotor rises, for example, to 100.degree. C., the bond strength of the permanent magnet is significantly reduced. Under such a situation, it is impossible to absolutely accommodate the demand for an increase in rotational speed of the motor.
On the other hand, in bonding the rotor body and the permanent magnets, it is considered that a brazing method having a large degree of freedom in selection of the bonding temperature is utilized. In this case, however, there is a possibility that cracks may be produced in the permanent magnet at a cooling step after a heating step, because the coefficient of linear thermal expansion of the steel rotor body is larger than that of the permanent magnet.